Conventionally, the starter motor of a self-propelled vehicle is a DC electric motor designed, on starting, to drive the shaft of the engine, e.g. by means of a sliding pinion that meshes with a driving ring carried by said shaft.
As is known, it is easy to start an engine by driving its starter by short circuiting the vehicle's contactor.
So solve this problem, it is known to fit vehicles with immobilization systems that prevent the engine from being started until an unlocking code signal has been received, e.g. by a computer controlling injection to said engine.
Nevertheless, injection computers are still not widespread, so at present few vehicles are fitted with such immobilization systems.